Originally posted by UKRobotics
*snip* I was told if I required 100W mechanical or less to use steppers or if it is 200W or more use servos and in between, either will do. Unfortunately that doesn’t mean much to me. I know how that translates into HP, but what I don’t know is how that translates into actual machining ability. Would I need a 200w or more motor
for milling ali or would 100 be ok ? And how greatly does motor wattage affect speed ? *snip* |
Power (designation P, unit watt [W] - and therefore sometimes called "wattage") is equal to speed times the force developed while moving.
For linear movement this is quite easy: power simply equals speed times force at that speed (in metric units: P [W] = v [m/s] * F [N]).
For rotary motion, it's really the same thing, but
1) you have to measure motor speed not in RPMs but in radians per second. This is called the "angular velocity" of the motor, designation
theta. 1 RPM = 2*pi/60 [rad/s]. So 1000 RPM equals about 104.7 rad/s.
and 2) you have to measure motor strength in torque (designation M, I think, and metric unit newton meter [Nm]).
Then power is simply (in metric units again): P [W] =
theta [rad/s] * M [Nm].
So a 100 W motor could be either 3000 RPM and 0.32 Nm (3000 RPM => about 314 rad/s * 0.32 Nm = 100 W), or 6000 RPM and 0.16 Nm, for example.
Observe that you cannot calculate the power of a stepper from its holding torque data. The holding torque is the torque at 0 RPM, and since power is torque times speed, you would end up with zero watts!
Originally posted by UKRobotics
*snip* As far as I'm aware, a servo motor is just a standard DC motor with an encoder attached. *snip* |
This is essentially correct. Servo motors are usually made to have a small rotary inertia (compared to "normal" motors), to be able to start and stop quickly. But this is mostly important for a production machine where every split second counts.
Hope this helps!
Arvid